1. Field of the Invention
The present invention relates to a system for controlling a reciprocating internal combustion engine having at least two intake valves per cylinder, such that the first valve is operated with a fixed duration event, and the second valve is operated with a variable duration event, with the timing of both of the valves being controllable and variable.
2. Disclosure Information
Charge motion control devices (CMCV) are sometimes used in conjunction with valve event timing retard to produce higher in-cylinder charge motion. Unfortunately, the CMCV may increase the engine's pumping losses, so as to undercut the fuel economy benefit produced by a variable cam timing (VCT) system. Moreover, even when in a wide-open position, most charge motion devices will cause a measurable flow restriction, which is translatable into a power loss. Charge motion control devices have limited operation ranges because of these pumping losses.
The inventors of the present invention have determined that excellent in-cylinder charge motion may be obtained with a two intake valve induction system without the need for a CMCV, if cam switching is used on one of the intake valves. As used herein the term “cam switching” means the provision of multiple, selectable, camshaft lobes for a single valve, such that the duration, lift, and even the timing of the valve event may be controlled. It has further been determined by the present inventors that a beneficial result will be provided in the event that intake camshaft retarding is used to place the opening of the secondary intake valve midway through the intake stroke, when the piston velocity has peaked and is proceeding to decrease. When the secondary valve is operated with a reduced duration and lift, a delay in secondary intake valve opening as opposed to primary intake valve opening occurs, such that at secondary intake valve opening the primary intake valve is at or near its midlift position. This lift staggering effect, coupled with the timing of the secondary valve opening relative to piston velocity biases most of the incoming air charge to flow past the primary valve. Biasing incoming air charge to one valve is similar to deactivating a valve and creates good in cylinder charge motion. In the present inventive system, a secondary intake valve is in essence operated with a lower event duration and lift so that flow is limited past the secondary valve and excellent charge mixing and charge motion occur because of the high airflow through the primary intake valve.
The Honda VTEC-E system which is employed without variable camshaft timing, switches a single intake valve from long to short duration and from a higher to lower lift to promote charge motion and mixing. Because the Honda VTEC-E system does not employ intake cam retard, flow past the secondary valve must be mechanically limited by using very short duration and low lift. This in turn impairs the efficiency of the engine.
A Honda cam switching mechanism itself may, however, be used as a component part of an engine according to the present invention, and U.S. Pat. No. 4,777,914, which describes such a mechanism, is hereby incorporated by reference into this specification.